A man has been arrested after igniting petrol inside his car and crashing it into the gate of a police station car park in Sydney.

The man, in his 60s, suffered serious burns in the incident in the suburb of Merrylands, but no-one else was injured.

New South Wales police said there is no indication that the incident was terror-related.

Assistant Commissioner Denis Clifford said t he man initially parked his car on the driveway of the police station and when an officer approached the vehicle, the man ignited an accelerant, which is believed to have been petrol, and drove into the roller door of the underground car park.

Police extinguished the fire and removed the unconscious man from the vehicle. He is now in a serious condition in hospital.

Mr Clifford said police are still trying to determine the man's identity and motivation.

"There's nothing to indicate this is in any way related to terrorism," he added. "We just don't know why this person has acted this way."

A bomb squad has inspected the vehicle, but there was no further threat to anyone, Mr Clifford added.

"The police reacted very bravely and it's just a miracle that no-one else was seriously injured," he said.